Thermoplastically processible molding materials with a high volume portion of magnetizable or permanently magnetic filler and a thermoplastic matrix are known.
Important fillers in this connection are rare earth metal compounds, such as Nd/Fe/B in polyamides, such as nylon-6, -11 and -12, or in polyphenylene sulfide or also in polybutylene terephthalate, as the matrix.
To attain satisfactory magnetic values, a volume portion of magnetic or respectively magnetizable filler of more than 30%, in particular of 50% or more, is necessary. This causes considerable problems in practical use, so that many solution attempts are proposed in the patent literature.
For technical areas of use, for example in the engine compartment of vehicles, the matrix properties are also of great importance.
In this connection, matrix materials with a satisfactory temperature resistance and methods for the sufficient mixture with the magnetic filler are particularly sought. Such methods are elaborate and expensive and take the environment only insufficiently into consideration.
With Nd/Fe/B compounds in particular, the so-called neodymium types, the problem of corrosion is added. The metallic neodymium particles corrode under the influence of moisture and/or oxygen. This reaction can even take place spontaneously and can lead to spontaneous combustion.
Therefore many methods are mentioned, in particular in the patent literature,
for delaying or respectively preventing the corrosion of neodymium particles, in particular by means of a protective coat, PA1 to modify the matrix by means of special additives, such as ester compounds or amide compounds of fatty acids to make it flowable and wetting-active, PA1 to bring the matrix into a form which allows a high degree of filling, for example fine grinding of the matrix or dissolving the matrix and coating the magnetic particles, with subsequent evaporation of the solvent, PA1 a1) 70 to 99 weight-% of a partially aromatic copolyamide with a melting point of more than 280.degree. C., and PA1 a2) 1 to 30 weight-% of an aliphatic polyamide or copolyamide with a statistical mean value of at least 10 --CH.sub.2 -- groups per --CONH-- group, and PA1 a3) 0 to 10 weight-% of property-relevant and/or process-conditional additives, PA1 wherein the sum of the matrix components a1) to a3) is 100% by weight, are preferred for this, in particular if their polyamide chain ends have an excess of amino end groups, e.g. NH.sub.2 groups and/or NHR' groups wherein R' is an alkyl radical or cyclohexyl radical, or the amino group is a component of a cyclo-aliphatic radical.
in order to make a matrix available which has special properties, for example satisfactory resistance to chemicals.
For example, Japanese Patent Publication JP 04 257203-A contains magnetizable neodymium particles, specially coated and provided with a bonding agent, in a PA-12 matrix containing magnesium stearate as the internal lubricant.
Japanese Patent Publication JP 03 270201-A describes a magnetic powder, such as Ba and Sr ferrite, in a linear polyamide, such as nylon-6, -66, 610, -11 and -12 as the matrix, which also contain bis-hydroxycarboxylic acid amides for improving processibility.
U.S. Pat. No. 4,462,919 describes the application of a coating on ferromagnetic samarium/cobalt, which is subsequently worked into a thermoplastic material, such as polyamide-12.
German Published Patent Application DE-OS 27 36 642 describes the addition of a thermoplastic material to oxidation-sensitive magnetic material as a solution under a protective gas.
Compositions are described in German Patent Publication DE 44 20 318 C2, which contain partially aromatic thermoplastic materials of the polyester and polyamide type and permanently magnetic and/or ferro-magnetic, metal-containing compounds.
With one exception, the thermoplastic compounds are polyester, in particular polybutylene terephthalate, which is present in pure form or as a polymeric alloy. A polymer identified as polyterephthalic acid hexamethylene diamide is used in Example 3 and described as having a melting point of 236.degree. C. However, the low melting point indicates that this must be a greatly modified product, because all customary partially aromatic polyamides (polyaramides) melt at a temperature of approximately 300.degree. C. and above. So a partially aromatic polyamide in accordance with the teaching of this patent can for example examplary be used, if it is present in a modified form such that its melting point, as described in the application example 3 as being 236.degree. C., has been substantially lowered.
As already explained and confirmed by DE 44 20 318 C2, the high-quality aromatic or respectively partially aromatic thermoplastic materials can only be used as a matrix for magnetic materials by means of processes which are expensive or of low environmental friendliness, such as fine grinding or application as a solution.
It is particularly difficult to produce thermoplastically processible magnetic materials with a high level of filling, in particular of more than 50 vol %, of magnetic or magnetizable metal compounds, in a matrix of partially aromatic polyamide with a melting point of more than 300.degree. C., and to process them.
Therefore thermoplastically processible magnetic materials are required, which have a matrix of dimensionally stable, hydrolysis- and chemically-resistant polyamide of high rigidity and a high melting point, which is filled to a high volume fraction, in particular of more than 50%, with a magnetic or magnetizable metal alloy and/or, which can be easily processed by means of injection molding and results in dimensionally stable magnetic or magnetizable molded parts.
Furthermore polymer based, thermoplastically formed parts of magnetic materials are required, preferably produced by injection molding, for special applications, for example electric motors, for use in automobiles or electronic entertainment devices, in particular if the continuous use temperature lies at 100.degree. C. or above, and temperature peaks of 200.degree. C. are temporarily attained.